Recent concern about preservation of the global environment has highlighted the need for reducing the fuel consumption of motor vehicles. Since an effective means of reducing the fuel consumption is to decrease the weight of the vehicle itself, this has stimulated the development of light-weight materials. Decreasing the weight of moving components in internal combustion engines for motor vehicles to improve power output performance and save fuel is therefore a matter of importance. For example, conrods are subjected to high temperatures and high loads, and so require high thermal fatigue strength, rigidity, and low thermal expansion. To meet these requirements, various types of aluminum materials have been tested.
The rapid solidifying powder metallurgy process allows extension of alloying levels and the aluminum alloy formed by this process has significantly improved the fatigue strength, rigidity, and thermal expansion compared to materials formed by the conventional ingot metallurgy process. As a result, various types of rapidly solidified aluminum alloys have been developed for moving components such as conrods in internal combustion engines which have excellent heat resistance, creep resistance, and abrasion resistance.
Most of those rapidly solidified aluminum alloys contain approximately 5 to 30% Si and 1 to 15% Fe. Such alloys are disclosed, for example, in JP-A-2-61021 and JP-A-3-177530 (the prefix "JP-A-" referred to herein means "unexamined Japanese Patent publication"). These rapidly solidified aluminum alloys have excellent rigidity and fatigue strength compared with conventional aluminum alloys prepared by the ingot metallurgy process. However, this type of Al-Si--Fe alloy still has poor fatigue strength around notches such as the root of a thread. Consequently, as illustrated in FIG. 1, a conrod of the alloy is prone to fatigue cracks at the corner edge 6 of the face receiving the bolt head or at a notch such as the root of the thread of the threaded hole 5 tapped into the rod 2 to receive the bolt which secures the rod 2 to the head 3 at the big end of the conrod 1. This poor strength causes problems in the practical application of the material for moving components such as conrods in internal combustion engines.